Final answer:
The narrative technique described is known as a flashback, which allows the author to present events out of chronological order to add depth to the story and characters.
Step-by-step explanation:
The narrative technique used by an author when they interrupt the main storyline to share a past incident, such as getting a new puppy in the context of a story about bringing a first child home, is known as flashback. This technique involves a shift in time to past events, which can provide background information, character motivation, or create a thematic connection. It is a way to introduce earlier events that are crucial to understanding the current actions or emotions of the characters.
Flashbacks are a common tool in both fiction and memoir writing used to create a deeper emotional connection with the reader. By presenting events non-chronologically, the author can construct a more compelling narrative that emphasizes themes or character development over a strict chronological order of events.